Sensor module, sensor system, and method for acquiring calibration value of sensor module

Abstract

To provide calibration means for a strain sensor suitable for a small sensor module that performs wireless communication.SOLUTION: A sensor module includes: a strain sensor; a Wheatstone bridge circuit including the strain sensor as one of resistors; an identification tag for radio frequency communication for communicating an output of the Wheatstone bridge circuit to the outside; a calibration resistor connected in parallel with the strain sensor in the Wheatstone bridge circuit and having a resistance value of the strain sensor before strain; and a switch for switching one of the resistors in the Wheatstone bridge circuit to either the strain sensor or the calibration resistor.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present invention relates to a sensor module, a sensor system, and a method for acquiring a calibration value of a sensor module. [Background technology]

[0002] The following Patent Document 1 discloses a sensor module offset cancellation circuit that cancels the offset voltage of a strain sensor in a sensor module having a sensor including a strain sensor. In this sensor module, a strain sensor (strain gauge) is attached to an object to be measured and used as a sensor that detects deformation of the object to be measured. The strain sensor forms a Wheatstone bridge circuit, and detects strain from a change in output voltage of the Wheatstone bridge circuit due to strain. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2007-208427 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, since strain sensors are subject to minute deformation when attached to the object to be measured, zero point correction (calibration) of the output value is necessary. Conventionally, zero point correction has been performed by adjusting the resistance of the strain sensor using a circuit separate from the Wheatstone bridge circuit. However, in the case of small sensor modules, the internal space of the module is limited, so it can be difficult to add parts and circuits for calibration.

[0005] In the above conventional technology, a controller is provided at the output of the Wheatstone bridge circuit to automatically calibrate the output value of the sensor module. However, because extra power is required to operate the controller, there is a problem that it is difficult to apply this technology to wireless devices equipped with RFID (Radio Frequency Identification) that operate with low power consumption.

[0006] The present invention has been made in consideration of the above problems, and has an object to provide a means for calibrating a strain sensor that is suitable for a small sensor module that performs wireless communication. [Means for solving the problem]

[0007] A sensor module according to a first aspect of the present invention comprises a strain sensor, a Wheatstone bridge circuit having the strain sensor as one of its resistors, an identification tag for radio frequency communication for communicating an output of the Wheatstone bridge circuit to the outside, a calibration resistor connected in parallel with the strain sensor in the Wheatstone bridge circuit and having a resistance value of the strain sensor before strain, and a switch for switching one of the resistors in the Wheatstone bridge circuit to either the strain sensor or the calibration resistor.

[0008] A second aspect of the present invention is the sensor module according to the first aspect, wherein the switch is a mechanical switch.

[0009] A sensor system according to a third aspect of the present invention includes the sensor module of the first or second aspect, and a terminal device that communicates with the sensor module via the identification tag.

[0010] A fourth aspect of the present invention may further include, in the sensor system of the third aspect, a memory unit that stores a calibration value of the output of the sensor module derived by switching the switch, a calculation unit that corrects the output value of the sensor module read by the terminal device based on the calibration value, and an output unit that outputs the output value of the sensor module corrected by the calculation unit.

[0011] A fifth aspect of the present invention is the sensor system according to the fourth aspect, wherein at least the calculation unit and the output unit among the storage unit, the calculation unit, and the output unit are provided in the terminal device.

[0012] A sixth aspect of the present invention is the sensor system according to the fourth or fifth aspect, wherein the storage unit is provided in an information management server capable of communicating with the terminal device.

[0013] A calibration value acquisition method for a sensor module according to a seventh aspect of the present invention includes a first step of attaching a sensor module of the first or second aspect to an object to be measured, a second step of operating the switch of the sensor module after the first step to switch one of the resistors of the Wheatstone bridge circuit to the calibration resistor, a third step of acquiring a first output value of the sensor module after the second step, a fourth step of operating the switch of the sensor module to switch one of the resistors of the Wheatstone bridge circuit to the strain sensor after the third step, a fifth step of acquiring a second output value of the sensor module after the fourth step, a sixth step of calculating a calibration value of an output of the sensor module based on the first output value and the second output value after the fifth step, and a seventh step of storing the calibration value after the sixth step. Effect of the Invention

[0014] According to the above aspect of the present invention, it is possible to provide a means for calibrating a strain sensor that is suitable for a small sensor module that performs wireless communication. [Brief description of the drawings]

[0015] [Figure 1] FIG. 2 is a diagram illustrating an example of use of the sensor system according to the first embodiment. [Diagram 2] 1 is a configuration diagram of a sensor system according to a first embodiment. [Diagram 3] FIG. 1 is a circuit diagram of a Wheatstone bridge circuit according to a first embodiment. [Figure 4] FIG. 1 is a functional block diagram of a sensor system according to a first embodiment. [Diagram 5] 4 is a flowchart showing a calibration value acquisition method for the sensor module according to the first embodiment. [Figure 6] FIG. 11 is a configuration diagram of a sensor system according to a second embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0017] (First embodiment) FIG. 1 is a diagram showing an example of use of a sensor system 1 according to the first embodiment. 1, the sensor system 1 includes a sensor module 10 attached to a measurement object 100, and a terminal device 20 that communicates with the sensor module 10. The measurement object 100 is not particularly limited, but examples thereof include pillars that support large structures such as bridges, roads, and buildings.

[0018] The sensor module 10 detects minute distortions of the measurement object 100. The sensor module 10 is attached to the measurement object 100 with, for example, an adhesive. Since the sensor module 10 is attached by hand, distortions inevitably occur during attachment. The sensor system 1 includes a means for calibrating the distortions that occur at the time of initial installation.

[0019] FIG. 2 is a configuration diagram of the sensor system 1 according to the first embodiment. 2, the sensor module 10 includes a strain sensor 11, a Wheatstone bridge circuit 12, an RFID tag 13, and a switch 30. The RFID tag 13 is an identification tag for radio frequency communication, and includes an RFIC (Radio-Frequency Integrated Circuit) 14 and an antenna 15.

[0020] The antenna 15 is formed of, for example, a 20 mm×70 mm metal foil pattern. The antenna 15 is connected to the RFIC 14. The RFIC 14 is connected to the Wheatstone bridge circuit 12 and is an IC package including an AC / DC converter that digitally converts the output value of the Wheatstone bridge circuit 12 (the sensor value of the strain sensor 11).

[0021] The RFID tag 13 performs wireless communication with the terminal device 20 by RFID. The wireless communication includes communication performed when the distance between the communicating devices is about several meters and the housings of the terminal devices 20 are in contact with each other. With this RFID, it is possible to supply power from one communicating device to the other device in a non-contact manner. Examples of such RFID-enabled terminal devices 20 include dedicated readers, as well as RFID-enabled smartphones, tablet computers, and notebook computers.

[0022] FIG. 3 is a circuit diagram of the Wheatstone bridge circuit 12 according to the first embodiment. 3, the Wheatstone bridge circuit 12 includes the strain sensor 11 as one of the resistors. Hereinafter, the side of the Wheatstone bridge circuit 12 to which the strain sensor 11 is connected is referred to as the measurement side 12a. The Wheatstone bridge circuit 12 includes resistors R1, R2, and R3 on each side other than the measurement side 12a.

[0023] At the measurement side 12a, the calibration resistor R4 is connected in parallel to the strain sensor 11. The calibration resistor R4 has a resistance value before the strain of the strain sensor 11. In other words, the calibration resistor R4 has an initial resistance value of the strain sensor 11, and has a resistance value that serves as a reference for calibrating the strain of the strain sensor 11 when it is attached.

[0024] The switch 30 switches the resistance of the measurement arm 12a of the Wheatstone bridge circuit 12 between the strain sensor 11 or the calibration resistor R4. When the switch 30 is operated to switch one of the resistors of the Wheatstone bridge circuit 12 to the calibration resistor R4, a calibration circuit as shown by A1 in Fig. 3(a) is formed. When the switch 30 is operated to switch one of the resistors of the Wheatstone bridge circuit 12 to the strain sensor 11, a measurement circuit as shown by A2 in Fig. 3(b) is formed.

[0025] The switch 30 is provided at the contact point of the calibration resistor R4. The switch 30 may be provided at a location other than the contact point of the calibration resistor R4, as long as the calibration circuit shown in Fig. 3(a) and the measurement circuit shown in Fig. 3(b) can be formed. The switch 30 is exposed on the surface of the sensor module 10, as shown in Fig. 2. The switch 30 is a mechanical switch, and can be manually operated after the sensor module 10 is attached.

[0026] 2 is a slide switch, but may be a push button, a toggle switch, a rocker switch, a rotary switch, etc. The switch 30 may be a relay switch. A relay switch consumes power when switching but does not consume power after switching, so it can contribute to power saving in the same way as a mechanical switch.

[0027] FIG. 4 is a functional block diagram of the sensor system 1 according to the first embodiment. 4, the sensor module 10 includes the above-mentioned strain sensor 11, a Wheatstone bridge circuit 12, and an RFID tag 13. The RFID tag 13 includes an RFIC 14 and an antenna 15.

[0028] The terminal device 20 includes a communication unit 21, a storage unit 22, a calculation unit 23, and an output unit 24. The communication unit 21 is an antenna device that transmits and receives high-frequency signals (RFID) with the antenna 15. The storage unit 22 includes memories such as an HDD, SSD, ROM, and RAM, and stores programs and various settings required for the operation of the terminal device 20, output values ​​and calibration values ​​(described later) of the sensor module 10, and the like.

[0029] The calculation unit 23 includes a CPU and performs calculations based on a program stored in the storage unit 22. The output unit 24 is a display of the terminal device 20 and displays the output value of the sensor module 10. The output unit 24 may be a speaker and output the output value of the sensor module 10 by voice, or may be a communication device for storing the output value and calibration value of the sensor module 10 in an information management server (not shown).

[0030] Next, a method for acquiring a calibration value (initial setting method) of the sensor module 10 in the sensor system 1 having the above configuration will be described.

[0031] FIG. 5 is a flowchart showing a calibration value acquisition method for the sensor module 10 according to the first embodiment. First, in this method, the sensor module 10 is attached to the measurement target 100 (first step s1). Since the sensor module 10 is attached by hand, distortion inevitably occurs during attachment.

[0032] Next, the switch 30 of the sensor module 10 is operated to switch one of the resistors of the Wheatstone bridge circuit 12 to a calibration resistor R4 (second step s2). This switching switches the Wheatstone bridge circuit 12 to the calibration circuit shown in Fig. 3(a). In this state, the communication unit 21 of the terminal device 20 is brought close to the RFID tag 13 of the sensor module 10 to acquire the first output value V0 of the sensor module 10 (zero point correction reference value of the strain sensor 11, see Fig. 2) (third step s3).

[0033] Next, the switch 30 of the sensor module 10 is operated to switch one of the resistors of the Wheatstone bridge circuit 12 to the strain sensor 11 (fourth step s4). This switching switches the Wheatstone bridge circuit 12 to the measurement circuit shown in Fig. 3(b). In this state, the communication unit 21 of the terminal device 20 is brought close to the RFID tag 13 of the sensor module 10 to acquire the second output value V1 of the sensor module 10 (initial strain value of the strain sensor 11, see Fig. 2) (fifth step s5).

[0034] Next, the terminal device 20 calculates a calibration value (zero point correction value) of the output of the sensor module 10 based on the first output value V0 and the second output value V1 (sixth step s6). For example, if the first output value V0 is "0" and the second output value V1 is "0.1", the calculation unit 23 calculates "-0.1" as the calibration value from the difference between the first output value V0 and the second output value V1. The storage unit 22 stores this calibration value (seventh step s7). With the above, acquisition of the calibration values ​​(initial settings) of the sensor module 10 is completed.

[0035] Thereafter, when measuring minute deformations of the measurement target 100 during a regular medical checkup or the like, the communication unit 21 of the terminal device 20 is brought close to the RFID tag 13 of the sensor module 10 to obtain the output value of the sensor module 10. At this time, the Wheatstone bridge circuit 12 is switched to the measurement circuit shown in FIG. 3(b). The calculation unit 23 reads out the calibration value from the storage unit 22, corrects the output value read from the sensor module 10 with the calibration value (e.g., "-0.1"), and outputs the corrected value to the output unit 24. The value output to the output unit 24 is an accurate value because it is a value obtained by calibrating the initial distortion of the strain sensor 11.

[0036] As described above, the sensor module 10 of the present embodiment includes the strain sensor 11, the Wheatstone bridge circuit 12 including the strain sensor 11 as one of the resistors, the RFID tag 13 for communicating the output of the Wheatstone bridge circuit 12 to the outside, a calibration resistor R4 connected in parallel to the strain sensor 11 in the Wheatstone bridge circuit 12 and having the resistance value of the strain sensor 11 before strain, and a switch 30 for switching one of the resistors in the Wheatstone bridge circuit 12 between the strain sensor 11 or the calibration resistor R4. With this configuration, a calibration circuit and a measurement circuit are formed in the Wheatstone bridge circuit 12, and the circuits can be switched by the switch 30, so that the strain sensor can be calibrated with a structure suitable for a small sensor module that performs wireless communication.

[0037] In the present embodiment, the switch 30 is a mechanical switch. This configuration eliminates the need for extra power to switch the switch 30, making the structure suitable for the sensor module 10 including the RFID tag 13 that operates with low power consumption.

[0038] The sensor system 1 of this embodiment also includes the above-mentioned sensor module 10 and a terminal device 20 that communicates with the sensor module 10 via the RFID tag 13. In addition, this embodiment is equipped with a memory unit 22 that stores a calibration value of the output of the sensor module 10 derived by switching the switch 30, a calculation unit 23 that corrects the output value of the sensor module 10 read by the terminal device 20 based on the calibration value, and an output unit 24 that outputs the output value of the sensor module 10 corrected by the calculation unit 23. In this embodiment, the storage unit 22, the calculation unit 23, and the output unit 24 are provided in the terminal device 20. According to this configuration, the calibration value information of the sensor module 10 can be stored on the terminal device 20 side, which is suitable for the sensor module 10 including the RFID tag 13 that operates with low power consumption.

[0039] In addition, the calibration value acquisition method of the sensor module 10 of this embodiment includes a first step s1 of attaching the sensor module 10 to the measurement object 100, a second step s2 of operating the switch 30 of the sensor module 10 after the first step s1 to switch one of the resistors of the Wheatstone bridge circuit 12 to a calibration resistor R4, a third step s3 of acquiring a first output value of the sensor module 10 after the second step s2, a fourth step s4 of operating the switch 30 of the sensor module 10 to switch one of the resistors of the Wheatstone bridge circuit 12 to the strain sensor 11 after the third step s3, a fifth step s5 of acquiring a second output value of the sensor module 10 after the fourth step s4, a sixth step s6 of calculating a calibration value of the output of the sensor module 10 based on the first output value and the second output value after the fifth step s5, and a seventh step s7 of storing the calibration value after the sixth step. This configuration enables calibration at the site where the sensor module 10 is installed, and can absorb variations due to radio waves and directional environment at the site.

[0040] Second embodiment Next, a second embodiment of the present invention will be described. In the following description, the same or equivalent configurations as those in the above-described embodiment are given the same reference numerals, and the description thereof will be simplified or omitted.

[0041] FIG. 6 is a configuration diagram of a sensor system 1 according to the second embodiment. 6, the sensor system 1 according to the second embodiment includes an information management server 200 capable of communicating with a terminal device 20. The information management server 200 includes a storage unit that stores a calibration value of the output of the sensor module 10, which is derived by switching the switch 30.

[0042] According to this configuration, even if the terminal device 20 that stores the calibration values ​​of the sensor module 10 breaks down or is lost, a new terminal device 20 can obtain the calibration values ​​from the information management server, and the new terminal device 20 can measure the strain of the measurement object 100. When there are multiple sensor modules 10, the information management server 200 may store the calibration values ​​in association with the identification information of each sensor module 10.

[0043] Although an embodiment of the present invention has been described in detail above with reference to the drawings, the specific configuration is not limited to this embodiment, and designs that do not deviate from the gist of the present invention are also included. [Explanation of symbols]

[0044] 1 Sensor System 10 Sensor Module 11 Strain Sensor 12 Wheatstone Bridge Circuit 12a Measurement side 13 RFID Tags 14 RFIC 15 Antenna 20 Terminal Equipment 21 Communications Department 22 Memory section 23 Arithmetic section 24 Output section 30 Switch 100 Measurement object 200 Information Management Server R1 Resistor R2 resistance R3 resistance R4 Calibration resistor s1 1st process s2 2nd process s3 3rd process s4 4th step s5 5th process s6 6th step s7 7th step V0 First output value V1 Second output value

Claims

1. A strain sensor; a Wheatstone bridge circuit including the strain sensor as one of resistors; an identification tag for radio frequency communication for externally communicating the output of the Wheatstone bridge circuit; a calibration resistor connected in parallel with the strain sensor in the Wheatstone bridge circuit and having a resistance value of the strain sensor before strain is applied; A switch for switching one of the resistors of the Wheatstone bridge circuit to the strain sensor or the calibration resistor. Sensor module.

2. The switch is a mechanical switch. The sensor module according to claim 1 .

3. A sensor module according to claim 1 or 2; a terminal device that communicates with the sensor module via the identification tag; Sensor system.

4. a storage unit that stores a calibration value of the output of the sensor module derived by switching the switch; a calculation unit that corrects the output value of the sensor module read by the terminal device based on the calibration value; an output unit that outputs the output value of the sensor module corrected by the calculation unit, The sensor system of claim 3 .

5. Among the storage unit, the calculation unit, and the output unit, at least the calculation unit and the output unit are provided in the terminal device. The sensor system of claim 4.

6. The storage unit is provided in an information management server capable of communicating with the terminal device. The sensor system of claim 4.

7. A first step of attaching the sensor module according to claim 1 or 2 to an object to be measured; a second step of operating the switch of the sensor module after the first step to switch one of the resistors of the Wheatstone bridge circuit to the calibration resistor; a third step of acquiring a first output value of the sensor module after the second step; a fourth step of operating the switch of the sensor module after the third step to switch one of the resistors of the Wheatstone bridge circuit to the strain sensor; a fifth step of acquiring a second output value of the sensor module after the fourth step; a sixth step of calculating a calibration value of the output of the sensor module based on the first output value and the second output value after the fifth step; and a seventh step of storing the calibration value after the sixth step. How to obtain the calibration value of the sensor module.

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